One of the (very) few things that managed to impress me at this year’s Mobile World Congress is the Asus Padfone. Sure, it’s not new. In fact the concept is almost one year old and still hasn’t shipped. But in a way I’m glad that Asus decided to wait one year and do this right. And I believe it has. Except for one thing, but we’ll get to that later.

In case you’ve been living under a rock for the past year, here’s the skinny: the Asus Padfone is an Android smartphone. Which can be docked inside a tablet. Which itself can be docked onto a keyboard. So it’s a smartphone, a tablet, or a netbook – whichever you prefer.

When the phone goes into the tablet, the UI is switched from a phone-centric one to a the usual Android tablet UI. This is undoubtedly thanks to Android 4 Ice Cream Sandwich bringing both experiences in the same package. The lack of such dual-mode functionality in earlier versions of Android may have been one of the reasons why Asus didn’t launch the Padfone last year.

The tablet bit is actually made up of a screen, a battery, speakers, antennas for Wi-Fi, GPS, and mobile network connectivity, and a front-facing camera. Because it has antennas built-in, you won’t lose any signal when inserting the phone into the tablet dock (it goes in all the way and is fully covered by a special flap when docked).

The tablet dock’s battery obviously charges the phone while it’s in there. And the tablet dock itself can be docked onto a keyboard, one very reminiscent of the one Asus uses for its Transformer tablets. Aside from keys and a touchpad, this dock also has a USB port (with full USB host functionality enabled), a headset jack, and a microSD card slot. The phone itself has another microSD card slot, so this is an additional one. So using the keyboard dock you can connect almost anything to the Padfone – camera, thumb drives, you name it.

This whole concept is extremely smart, and it works. Snapping the phone into the tablet and the tablet into the keyboard (and taking them out) will take some getting used to, but not more than a couple of days I think.

So what’s the problem then? Well, despite having well over 10,000 mAh of total battery capacity between the phone, tablet, and keyboard dock, the phone itself only comes with a 1,500 mAh battery.

That, for a high-end Android smartphone, was almost bearable last year and the year before. In 2012 though it’s simply not enough. It would be hard to name one other manufacturer that has launched a new flagship smartphone with this capacity battery in the past few months. And that’s for a good reason, too. With today’s huge screens it’s impossible for such a small battery to make it through even one day.

I have a feeling that Asus thinks you’ll just dock the smartphone into the tablet sooner than you would otherwise charge your smartphone, but this still isn’t an ideal solution. Especially since an Asus rep told me that they are considering offering the phone component by itself too in some markets. Sure, there will be bundles with the tablet (mostly) or even with the keyboard dock as well in some places, but – viewed exclusively as a smartphone, and ignoring the docks, the Padfone simply doesn’t cut it, runtime-wise, in this day and age.

Which is really sad. So sure, at home or work you may dock it into the tablet since that can be used for some things easier than a phone anyway, but when you’re out and about I doubt you’ll want to always carry the tablet dock with you as a spare battery of sorts.

Which is why I won’t be buying one of these. However, if you feel like you’ll dock the phone in the tablet at least once throughout your day (and leave it there for a couple of hours too), then this may be for you. If so far you’ve been wary about getting a tablet alongside your smartphone, perhaps next time you upgrade you’ll get the Asus Padfone so you won’t have to then buy a separate device.

The phone+tablet combo should cost somewhere around £450 in the UK, so about €530. That’s unsubsidized, of course. The phone by itself should come in at under £400, the tablet dock accessory retailing for around £70-80. But, again, I seriously can’t recommend the Padfone if all you’re getting is the phone.

In fact, you should probably consider the keyboard dock too, alongside the tablet one. Especially if you do a lot of actual creating content, and not just consuming it (for which the tablet is more than sufficient).

The neat thing here is that because all the data is on the phone, different members of the same family can, for example, use the same tablet dock (not at once, though). Simply taking the phone out of the tablet dock when you’re done using it is a lot easier than sharing ‘normal’ tablets between multiple users.

Oh, and the ‘one more thing’ moment from Asus is an interesting capacitive stylus for the Padfone which doubles as a Bluetooth headset so you can speak on the phone while it’s docked. All pretty amazing really – although you will look strange holding what looks like a pen up to your ear.

All of this will apparently be out sometime in April. So start saving.